Can't use my own Phone

I need big help with this lil problem I'm having with my Iphone. Some info:

Iphone 3gs
Jailbroken
5.1 ioS
baseband 05.16.05

Ok. so I think it's unlocked. I recently changed my old phone to this one so i bought a sim card for it. And it either says searching indefinitely or no service. I cannot use my phone. Please any help would be great as I currently have no phone.

Thank you

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Also forgot to add. I've tried a lot of things like taking the sim card in and out.
resetting network data, re-installing ultrasnow and Sam. 3g on and off. Air plane mode on and off.

Also when I go into setting. about. network. says not available. scroll down to carrier and it shows the carrier of the sim card (but still cant use it).
or I go into settings. carrier, and its automatic on. if I go to turn it off it says unable to load network list.

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